Nest- no power to Rh with common connected
#1
02-23-17, 04:48 PM
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Nest- no power to Rh with common connected
Hello! first time poster so please be gentle.
I recently bought a Nest for my home. Furnace is a Lennox 80UHG with a Surelight Integrated control board.
When I removed the old thermostat, the wires were connected to W1, Rh and G. The Nest would not stay charged, so I read enough to realize I would need a common wire. There were additional wires in the cable, but they were not hooked up at either end. So I opened the furnace, and connected the spare blue wire to the C terminal on the control board.
When I hook up the blue wire to the C terminal on the Nest base, I get the red symbol indicating no power to Rh...but if I remove the common, it all works fine
Any ideas what could be causing this?
Thanks
I recently bought a Nest for my home. Furnace is a Lennox 80UHG with a Surelight Integrated control board.
When I removed the old thermostat, the wires were connected to W1, Rh and G. The Nest would not stay charged, so I read enough to realize I would need a common wire. There were additional wires in the cable, but they were not hooked up at either end. So I opened the furnace, and connected the spare blue wire to the C terminal on the control board.
When I hook up the blue wire to the C terminal on the Nest base, I get the red symbol indicating no power to Rh...but if I remove the common, it all works fine
Any ideas what could be causing this?
Thanks
#3
02-23-17, 05:17 PM
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Yep, I tried that, in fact the original wiring was to the Rc terminal with a jumper to the Rh. Nest internally jumpers the Rc and Rh, so it made no difference.
#4
02-23-17, 07:35 PM
Group Moderator
You either have a defective nest or the 24vac is sagging.
Use a meter to check from C to R at the board when the nest is connected and not connected.
Use a meter to check from C to R at the board when the nest is connected and not connected.
#7
02-24-17, 09:26 AM
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The wire colours at the control board all match up with the base.
When I took the original thermostat off, the Rh and the W1 wires were the wrong way around. I did not know this at the time, so I hooked the Nest up the same way, and it worked fine (but no charging). Since reading about this, I noticed they were reversed, so I swapped them. The Nest still does the same thing, no matter which way round R and W are. It works, but does not charge, and connecting the C wire stops it working.
When I took the original thermostat off, the Rh and the W1 wires were the wrong way around. I did not know this at the time, so I hooked the Nest up the same way, and it worked fine (but no charging). Since reading about this, I noticed they were reversed, so I swapped them. The Nest still does the same thing, no matter which way round R and W are. It works, but does not charge, and connecting the C wire stops it working.
#9
02-24-17, 11:18 PM
Group Moderator
Based on the voltages you measured.... the stat is not charging.
I'd say the nest has a problem with it's charging circuit.
I'd say the nest has a problem with it's charging circuit.
#11
02-25-17, 06:02 AM
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@Astuff...there are additional wires, I had tried the orange initially and am now on the blue, so it's not that.
@PJmax, Houston204, thanks, I will contact Nest about this.
@PJmax, Houston204, thanks, I will contact Nest about this.
#12
03-15-17, 02:37 PM
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All fixed, Nest sent a replacement baseplate which seems to have fixed the issue...thanks for your help guys.
#13
03-15-17, 03:32 PM
Group Moderator
Thanks for letting us know how you made it out. 
It's especially helpful to others that have or will have the same problem.
It's especially helpful to others that have or will have the same problem.
#14
03-15-17, 04:03 PM
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I've been the guy trying to solve a problem and finding dead threads...didn't want my thread to end up that way...
https://www.xkcd.com/979/
https://www.xkcd.com/979/
